Convert excel datetime text to a sort-able standard datetime string

Here are a few excel datetime strings in format like “m/d/yyyy h:mm:ss am/pm”, so the length of this string is different in different date/time:

• 2/3/2017 8:2:32 AM
• 12/23/2017 1:20:32 PM

Searched a little bit seems there’s no result to convert these examples to a standard sortable string in format like: “yyyy-mm-ddThh:mm:ss”, have to make one